In cryogenic coolers of the type which has a compressor pressure wave driven free displacer, or regenerator-displacer, friction seals are generally used between the moving free displacer and the housing. When the friction seals are new, the movement of the free displacer occurs at or near the extremities of the pressure waves providing maximum work and thus maximum refrigeration. However, as the friction seals wear, there is less frictional restraint exerted by the seals and the free displacer will move even when very little force is applied by the pressure valves. Therefore, movement of the free displacer occurs prior to the pressure wave extremes, and thus less work and less refrigeration is done within the cooler.